We are surrounded by a considerable number of products that utilize electromagnetism, such as transformers, motors, generators, speakers, inductive heaters, and various actuators. Many of these products utilize an alternating magnetic field and are usually provided with a magnetic core (soft magnet) in the alternating magnetic field in order to obtain a large alternating magnetic field locally and efficiently.
Magnetic cores are required not only to have high magnetic properties in an alternating magnetic field but also to have a less high-frequency loss (referred to as an “iron loss,” hereinafter, regardless of the material of magnetic core) when used in an alternating magnetic field. Examples of the iron loss include an eddy-current loss, hysteresis loss, and residual loss, among which the eddy-current loss is important and should be reduced because it increases as the frequency of an alternating magnetic field increases.
As such magnetic cores, powder magnetic cores are researched and developed, which are obtained by compression molding of soft magnetic particles (constitutional particles of powder for magnetic cores) that are each coated with an insulating layer (film). The powder magnetic cores are used in various electromagnetic devices because the insulating layers lie between the soft magnetic particles thereby to achieve a high specific resistance, low iron loss, and high degree of freedom in the shape. In recent years, to expand the uses of powder magnetic cores, enhancement of the strength is focused on together with the specific resistance. Descriptions regarding such powder magnetic cores are found in the patent literature below, etc.